Behavior of trypsin and related enzymes toward amidinophenyl esters

Kinetics of the hydrolysis of amidinophenyl esters catalyzed by urokinase, kallikrein, plasmin and trypsins from various origins were studied. P-Amidinophenyl esters in which the arrangement of the specific group for bovine trypsin (charged amidinium) is reversed to that of normal substrates were characterized as specific substrates for the enzyme and named "inverse substrates" (K. Tanizawa, Y. Kasaba and Y. Kanaoka, J. Am. Chem. Sc., 99, 4485-4488) Behavior of these enzymes toward amidinophenyl esters was demonstrated to be very similar to that of bovine trypsin. These observations account for the structural similarity of their active sites. p- Amidinophenyl esters were found to be hydrolyzed also by clostripain which is known as a thiol protease with trypsin-like specificity. This is the first example of the "inverse substrates" for a thiol enzyme.